The FSIS Chemistry Laboratory Guidebook method Screening and Confirmation of Four Nitrofuran Metabolites by Liquid ChromatographyTandem Mass Spectrometry has been updated. See the method at:
http://www.fsis.usda.gov/wps/wcm/connect/9104c880-cf55-4b30-90b6-8d3f60c22a01/CLG-NFUR3.pdf?MOD=AJPERES